On-chip voltage regulators are switching voltage regulators employed for regulating and controlling a voltage supply of digital logic circuit such as, for example, a microcontroller, a microprocessor and a microcomputer. Such on-chip voltage regulator circuits typically convert an unregulated input voltage into a regulated output voltage of a predetermined value determined by a reference voltage to the regulator. Upon applying the input voltage to the switching voltage regulator, there is inrush of current which may damage the power devices, inductor and capacitor employed in switching voltage regulator. Start-up circuits can be employed in such switching voltage regulators to ramp the output voltage from zero value to a predetermined value without causing the current exceeding the maximum limit.
Most prior art start-up circuits with respect to the switching voltage regulators employ an input/output (I/O, package pin) pin and a fixed frequency clock for performing the start-up. Such input/output (I/O) pin can be employed to slowly ramp the reference voltage to the switching voltage regulator from zero value to a predetermined value. The switching voltage regulator compares this slow ramping reference to its output voltage every fixed frequency clock. By virtue of this mechanism, the output voltage is ramped to its predetermined value without current exceeding the maximum limit.
Based on the foregoing, it is believed that a need exist for an improved start-up system and method for switching voltage regulators without the input/output (I/O) pin and clock for startup, as described in greater detail herein.